1. Field of the Invention
The present invention relates to an organic electro-luminescent display (OLED) and a method of forming the same and, more particularly, to a top-emission OLED and a method of sealing the same.
2. Description of the Related Art
In the new generation of flat panel techniques, organic electro-luminescent display (OLED) has advantages of self-luminescence, wide-view angle, thin profile, lightweight, low driving voltage and simple process. In OLEDs with a laminated structure, organic compounds such as dyes, polymers, or other luminescent materials serve as an organic luminescent layer and are disposed between cathode and anode. In accordance with the driving mode, OLED is classified into passive matrix and active matrix types. Alternatively, in accordance with the luminescent path, OLED is classified into a bottom-emission OLED and a top-emission OLED. Conventionally, both of the passive and active matrix types are fabricated as the bottom-emission OLED in which glass material is used to form the luminescent faceplate and transparent conductive material is used to form the anode layer. Thus, when electrons and holes are combined as excitons in the organic luminescent layer, light radiates from the transparent faceplate. However, since the luminescent regions of the R, G and B are different within each pixel area, TFT structures in array have different sizes and thus reduce the aperture ratio of the bottom-emission OLED.
In order to increase the aperture ratio, a top-emission OLED is developed in which the cathode layer is transparent materials and a transparent faceplate is sealed on the top of the OLED. FIG. 1 is a sectional diagram showing a conventional top-emission OLED. The top-emission OLED 10 has TFT devices and circuit devices completed in the substrate 10. On the substrate 10, a lengthwise-extending anode layer 12, an organic electron-hole transmitting layer 13, an organic fluorescent film 14, an organic electron transport layer 15, a transversely-extending cathode layer 16, a barrier layer 17 and a transparent faceplate 18 are successively formed. When avoltage is applied to the top-emission OLED, electrons and holes are relatively removed to the organic fluorescent film 14 to radiate light from the transparent faceplate 18. The direction of radiation is shown as the arrow. Therefore, the size of the TFT device does not affect the luminescent faceplate 18, and the materials of the substrate 10 can be selected from glass, silicon, ceramic materials, or plastic materials.
However, as the duration of use increases, the probability of moisture and oxygen permeating the OLED also increases, causing detachment between the organic luminescent layer 14 and the cathode electrode 16, cracking of the organic materials, and oxidation of the electrodes. As a result, a so-called “dark spot”, to which electricity is not supplied, is generated, decreasing luminescence and luminescent uniformity. Accordingly, in conventionally sealing the top of the top-emission OLED, one method uses a glass plate to isolate moisture/oxygen from the outer environment, but the glass plate with large volume and weight does not fit the requirements of the OLED. The other method coats a UV-curing resin on the top of the top-emission OLED to provide a transparent result, but the resin with outgassing phenomenon and poor resistance to moisture cannot assure the luminescent property of the OLED. Thus, a novel sealing structure of the top-emission OLED solving the aforementioned problems is called for.